The invention relates to a device for joining metal sheets by a rivetting-type method utilizing mating dies in which the counter-edges provided by a female die are yieldable.
Such a device has been disclosed by German Offenlegungsschrift No. 3,106,313. In this device two levers carrying the counter-edges are arranged next to the anvil of the female die. The levers are pivotable about axes running transversely to the lifting direction of the press, and a helical compression spring acts on the two levers in such a way that they are biased into the cutting position in which they bear against the anvil. The linear distance of the two lever pivoting axes is greater than the distance of the two cutting edges of the punch.
A device of the same generic type has also been disclosed by U.S. Pat. No. 2,288,308. In this case, the female die comprises a plurality of components: a base; an anvil tapering towards its free end extends from the base; and counter-edge elements in the form of perforated steel plates supported on the base, bearing against the inclined side faces of the anvil. A bolt is also provided through a bore, on which spring discs acting on the outside of the steel plates are seated. The distance of the plate rims or counter-edges from the base on which the plates are supported and around which they tilt when yielding laterally, is thus greater than the distance of the cutting edges and counter-edges in the rivetting position.
The same comments apply to the embodiment according to U.S. Pat. No. 2,254,558; in the embodiment illustrated therein, the cutting edge bodies and the return leaf spring are integrally formed, angled off or bent off, and the cutting edge bodies are supported by the anvil.
In the known constructions described, it is found that, during the cutting through the two sheets, a force component directed inwards onto the anvil is exerted onto the components provided with the counter-edges--that is to say the levers or plates--which ensures that the counter-edges do not already yield laterally during the cutting-through phase.
On the other hand, however, this has the consequence that in the second phase of flow-pressing the counter-edges not only yield laterally but, during their yielding movement, also have a component which is directed towards the punch and which has a tendency to prevent the joint made from reaching that strength which ought to be possible under otherwise identical conditions. Moreover, chips could penetrate between the cutting edge components and the portions of the anvil supporting the former, whereby the usefulness of the entire device is put into question. It should be desirable, rather, that the elements provided with the counter-edges would move away precisely laterally.
This might perhaps be achievable constructionally by an appropriate sliding mount of the components provided with counter-edges and by springs acting perpendicular to the lifting direction of the press. This would, however, not only result in an expensive and complicated structure, but also in an even greater lateral extension of the female die than appears to be unavoidable even in the most modern known construction according to the German Offenlegungsschrift initially mentioned.